Method of making bessemer or converter steel



United States Patent METHOD OF MAKING BESSEMER OR CONVERTER STEEL Edwin 'C. Wright, University, Ala., assignor to Pennsylvania Engineering Corporation, New Castle, Pa., a corporation of Pennsylvania i No Drawing. Application March 17, 1953 Serial No. 342,910 r I 4 Claims. (Cl. 75-46) the best steel made by open hearth and electric furnace procedures.

In accomplishing this object I employ a two step procedure. One in which silicon, manganese and a part of the carbon contained in the bath of molten pig iron is reduced in an acid lined converter by a bottom blow, and the other in which the phosphorus and also the carbon remaining in the molten bath are reduced in a basic lined converter by a side blow. I, however, depart from all old procedures by reducing the temperature of the bath after the bottom blow from about 1750-1850? C. to a C. as a preliminary to intemperature of about 1420 itiating the sideblow in the basic lined converter. This reduction in temperature is preferably accomplished at the end of the first step by adding sufiicient steel scrap to the molten bath in the acid lined converter and preferably before the slag on the bath has been removed. After the bath is so cooled and the slag is removed therefrom, the molten metal is delivered to a side blow basic lined converter in which the phosphorus content of the bath and the carbon remaining in the bath are reduced.

' Around 1884, several installations were made which involved the use of two Bessemer converters. One of these was in France and the other in Luxembourg. In each of these installations, the first stage converter was acid lined, while the second stage converter was basic lined. In these installations, both converters were side blown and each was relatively small, being of about two tons capacity. These early experimental installations are referred to in a paper entitled The Development of the Bessemer Process for Small Charges found on page 846 of the Transactions of American Institute of Mining Engineers, 1903, vol. XXXIII, but they have left no impress on the commercial art.

. For many years the Bessemer method of making steel in acid lined Bessemer converters led all other methods in this country. At the present time, however, the amount of Bessemer steel made in this country is not more than about 5% ofthe total steel produced; approximately95% being made by other methods or processes which are much slower and much more expensive.

The terms side blown or side blowing and bottom blown or bottom blowing as used herein refer to the manner in which the air is introduced to the bath of molten pig iron. Bottom blowing or bottom blown means that the air blast passes through the molten metal within the converter. It is generally introduced through the bottom ,of the converter, but in a tilting converter, it maybe introduced through one side of the converter but under conditions such that when the converter is tilted vent the temperature of the bath from 2,875,037] Patented Feb. 24, 1959 it passes upwardly through the molten metal. Side blowing or side blown means that the air is introduced above the surface of the molten metal in the converter, impinges on the surface thereof, but does not pass through the metal.

I have discovered that I can make Bessemer steel which is extremely low in nitrogen (.005 and of a quality equal to any made by the basic open hearth method, in relatively large converters (for example 30 tons capacity or more) from molten in phosphorus.

No one prior to my invention has succeeded in making low nitrogen, low phosphorous Bessemer steel. Low nitrogen Bessemer steel has been produced by side blowing in an acid lined converter. Low phosphorus Bessemer steel has been produced by bottom blowing in a basic lined converter, but no one has produced a com mercially practical procedure for making Bessemer steel which is low in both nitrogen and phosphorus. Phosphorus cannot be removed in an acid lined converter. It may be oxidized by bottom blowing in a basic lined converter if the amount of phosphorus in themolten bath exceeds 1.50% and if the silicon content is below 0.75%, and sufiicient lime is added to the slag to hold the phosphorus. If, however, the silica content of the slag is high, as for example, from pig iron having over 1.00% silicon, removal of phosphorus is very erratic. Low silicon, high phosphorus pig iron is available in England but is not available in the United States and this is necessary for carrying out a Bessemer procedure such as is used in England in producing low phosphorus, high nitrogen steel, but steel which will not meet many of the American steel specifications.

I am able to produce high grade steel of the extremely low nitrogen content mentioned (less than 0.005%), in commercial quantities and under commercial operating conditions, by employing a two stage or duplex procedure. As previously stated, I utilizea bottom blow acid lined converter in removing the silicon and manganese and a part of the carbon from molten pig iron. I then employ a side blow basic lined converter for reducing the phosphorus and the remaining carbon and for thereby completing the production of high quality Bessemer steel.

In carrying forward this procedure it is important to use a bottom blow acid lined converter for the first stage trol is necessary because of the heat produced during the side blow of the second stage. The temperature of the bath rises rapidly during the bottom blow of the first stage. In order to prevent rapid disintegration of the lining of the converter employed, it is desirable to pre- During the firststage the temperature is controlled, at least to some extent, by the passage through the bath of the large volume of the nitrogen content of the air employed during the bottom blow. Then too, during the bottom blow the combustion of the carbon produces carbon monoxide gas, Whereas during the side blow the resulting combustion produces carbon dioxide gas, with the result that the heat generated in the side blow converter occasions an extremely rapid increase in the temperature of the bath and it is, therefore, necessary to provide a temperature control effective during the side blow in order to produce the low nitrogen, low phosphorus steel such as is here contemplated and at the sametime prevent rapid disintegration of the'converter pig iron which is either high or low greatly exceeding second stage is shown in Table germs? in the side blowing operation and it is necessary to cool the metal by the addition 15,000 pounds of steel scrap will absorb about 10,000,000 B. t. u. in being heated to 1700 C. If this is added to the 60,000 pounds originally charged a resulting bath of about 75,000 pounds of molten metal will be obtained with a total heat content of 36,398,28013. t. u. The calculated temperature is then 1420 C. which is just about the desired initial temperature for successful side blowing. The molten bath as cooled is transferred to a basic lined side blown vessel and blown until the carbon flame disappears, at which time the phosphorus and carbon will" be reduced to below 0.04%. Sufficient burned lime is charged before the'side blowingis started to combine with the known quantity of phosphorus to hold this impurity in the slag. The carbon content of the metal before-side blowing is 2.74% and the phosphorus content is 0.20% after dilution by the cold scrap addition.

If 25,000 cubic feet of air per minute is supplied to the side blow converter, it will require 12.5 minutes to furnish the oxygen necessary for the oxidation ofthe 2052# of carbon, 150# of phosphorus and 500# of iron which will be oxidized in this final side blowing stage.

of cold scrapiron or steel.

The heat generated by these reaction will be 19,985,500

B. t. u. while the radiation losses and sensible heat of the gases will absorb 14,844,160 B. t. n. This will cause a net gain of 5,141,340 B. t. u. which will bring the temperature of the finished 'bath to 1640 C. This is a very desirable temperature for casting steel ingots It will be seen from this example that a suitable means of regulating the temperature of the bath is available at each stage by varying the scrap added to take up the excess heat developed in the initial stage which is carried out in an acid lined converter.

It is believed that there will always be a need for approximately 25% cold iron or steel scrap addition to the bottom blown metal before the final stage of side blowing. This amount is just about the normal amount of home scrap that every steel plant produces in rolling its own ingots. In this sense my two stage Bessemer process is balanced as to raw materials as the plant would not have to buy outside scrap to make steel nor would it have a surplus of scrap to be disposed of to outside customers.

The extent of the phosphorus concentration in the H. Here the amount of calcium phosphate formed from pig iron charges of various phosphorus content is disclosed. There will always be some dilution of this slag from the MgO (magnesia) of the basic lining of the converter in this side blown stage.

My process is not limited to the use of ton capacity converters such as are referred to in describing the embodiment of my invention. There is no reason why much larger converters cannot be used in the processing of much larger batches of molten pig iron, and it will be apparent that my invention provides an economical and highly eflc'ective method of making Bessemer steel which has an exceedingly low nitrogen content (.005 and a low oxygen content (003%) and is of a quality equal to any steel made by the basic open hearth process. It is also apparent that my novel method not only produces Bessemer steel of superior quality, but also produces two valuable slags, i. e., an iron, manganese, silica slag and an iron, calcium phosphate slag, one of which is suitable for use in the recovery of manganese, while the other is a limey slag of high phosphorus content substantially free of silica, and, as previously noted, highly valuable as a fertilizer.

The life of the linings of the converters used in carrying out my novel Bessemer process will be greatly in creased over the life of either the acid or basic lined Bessemer converters now in use and of equal tonnage, and the process results in an economically produced high quality steel and the two slags, each of which is commercially valuable.

Figures based on blowing 60,000 pounds of pig iron at times indicated using 25,000 cubic feet or air per minute.

TABLE 11 Slag composition with pig irons of various phosphorus a contents Phospho- P OaO Calcium ms in Formed Needed Phosphate Time of Blow for Pig Iron, Side Blow For Formed, About 3% O percent Stage, Slag, pounds pounds pounds 1 0.25 a 345 p 397 742 AboutZO Minutes. 0. 50 690 794 1, 484 About 23 Minutes. 1.00 7 1,380 1,588 2,068 l About 30 Minutes.

Figures based on blowing 00,000 pounds of pig iron at times indicated using 25,000 cubic ieet of air per minute.

What I claim is:

1. A method of making Bessemer steel having a nitrogen content of not more than 0.005% content of less than 0.04%, which consists in blowing with air a bath of molten pig iron in an acid lined converter until substantially all the silicon and manganese of the bath is oxidized and the carbon content of the bath is reduced to not more than 3%; reducing the temperature of the bath and of the slag contained thereon to about 1500 C. by adding to the bath through the slag a calculated quantity of cold iron and steel scrap; removing the thus partially cooled slag from the bath; transferring the slag-free molten metal from the acid lined converter to a basic lined converter; covering the bath in the basic lined converter with basic slag-forming material; side blowing the bath in the basic lined converter to further reduce the carbon content thereof and to the extent that phosphorus content is reduced below 0.04%; and then in separating the resultant slag from the finished steel constituting the molten bath.

2. A method of making Bessemer steel having a nitrogen content of not more than 0.005 and a phosphorus content of not more than 0.04% and tWo types of commercially valuable slags, which consists in delivering a bath of molten pig iron to an acid (silica) lined converter; bottom blowing such bath in such converter with air to the extent that substantially all the silicon and manganese thereof is oxidized and the carbon content thereof is reduced to not more than 3%; cooling the bath and the supernatant slag after such blow by delivering a calculated amount of cold ferrous metal scrap thereto; removing the iron-manganese-silicate slag from the surface of the bath after such cooling and delivering the cooled, slag-free metal to a basic lined converter; covering the surface of the molten metal bath in such basic lined converter with basic slag-forming material containing calcium oxide; then side blowing the bath in said basic lined converter to further reduce the carbon content thereof and to the extent that the phosphorus content of the bath is reduced to at least 0.04%; and then removing the phosphate containing calcium slag from the bath.

3. A method of making Bessemer steel containing not and a phosphorus A more than 0.005% nitrogeri'and less than 0.04% phosphor u's" while p'ro'd-uci'rlg 'two conime'rcially valuable slags, which consists in delivering a bathf'mol't'en' pig iron to an acid (silica) lined con-verten bottom blowing such bath with air to the extent of removing substantially all the silicoh aiid manganese content thereof and of reducing the carbon content to manure than 3%; cooling the metal bath and' the slag formed thereon to a temperature of approximatelyil'420 C, by delivering a suflicient quantity of cold ferrous metal theret'o th'rough such slag; removing the thus" cooled iron-manganese' silicate slag from the bath; delivering the slag-free molten metal bath to a basic lined con'vr-terf; covering" the surface of such bath in suchflconverteruwith calcium oxide; then side blowing the bath 'w ith sufficient air to' reduce the carbon content thertiflt'd riot mare than 0.04 and the" phosphorus content to not more than 0.04%; then removing the phosglutamat -containing; calcium slagafrom the bath.

4. A method of makingBe'ssefrinstl containing not more than 0.005% nitrogen and less than 0.04% phosphorus while producing two commercially valuable slags, which consists iri delivering a bath of molten pig iron to an acid (silica) lined converter;- blowing such bath to the extent of removing substantially allthe silicon and mangjanese content thereof and of partially reducing the carljoncontent thereof; cooling the metal bath and the slag formed thereon to a temperature of approximately 1420 C. by delivering a sufficient quantity of cold'fenfous metal thr'et'o'th'r'ough: such slag" to accomplish such cooling; separating 'thetltus cooled slag from thebath; delivering the slag' fre'e molten metal bath to a basic'lined converter;

5 thefiseparating' thslagfifiiti thebatli; J

covering the surface of such bath in such converter with basic slag-forming material; menside' blowifigth'e'batlf'to the extent thatbdth the carbon cdntentand the phqs phdrus content thereof is r'uncedto not rfiore #0203 75 References Gitedin the file of this patent UNI FED SiTATESPA'IEN'l-S 211,962 .rh riias' nn gzg, "f

1278;7312' eese 1'J'fin s, 2 7,842 McDonald lflbvtj's;

695,256 White Mar. 1 1', I 2,207,30 W ,9 9 24) 2,218, 8 2 --O 5 12 2139 346 j, Dec-1,419. 5 .2' ,49jo,290 Worli 6.1 11949 2501,33; stay FOREIGN PATENTS .521 Great Britain Fe'b, 14437 9 L633 Great Britain 'A 5f.' 29',187'9 ofgsza Y a V.

7 18,01 Great Brit'ain' t Mayan, 1912 011911 i V OTHER REFERENCES Journal of- The Iron and SteellI nstit'tit; vol; 157,15:ag'e

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pages 339 358 5. only age 34oi'sr'elidoii. V r 

1. A METHOD OF MAKING BESSEMER STEEL HAVING A NITROGEN CONTENT OF NOT MORE THAN 0.005% AND A PHOSPHORUS CONTENT OF LESS THAN 0.04%, WHICH CONSISTS IN BLOWING WITH AIR A BATH OF MOLTEN PIG IRON IN AN ACID LINED CONVERTER UNTIL SUBSTANTIALLY ALL THE SILICON AND MANGANESE OF THE BATH IS OXIDIZED AND THE CARBON CONTENT OF THE BATH IS REDUCED TO NOT MORE THAN 3%; REDUCING THE TEMPERATURE OF THE BATH AND OF THE SLAG CONTAINED THEREON TO ABOUT 1500*C. BY ADDING TO THE BATH THROUGH THE SLAG A CALCULATED QUANTITY OF COLD IRON AND STEEL SCRAP; REMOVING THE THUS PARTIALLY COOLED SLAG FROM THE BATH; TRANSFERRING THE SLAG-FREE MOLTEN METAL FROM THE ACID LINED CONVERTER TO A BASIC LINED CONVERTER; COVERING THE BATH IN THE BASIC LINED CONVERTER WITH BASIC SLAG-FORMING MATERIAL; SIDE BLOWING THE BATH IN THE BASIC LINED CONVERTER TO FURTHER REDUCE THE CARBON CONTENT THEREOF AND TO THE EXTENT THAT PHOSPHORUS CONTENT IS REDUCED BELOW 0.04%; AND THEN IN SEPARATING THE RESULTANT SLAG FROM THE FINISHED STEEL CONSTITUTING THE MOLTEN BATH. 